Resuscitation, as that term is herein used, refers generally to externally exerted efforts to assist or restore breathing of a patient whose natural breathing has either become impaired or has ceased, or to at least temporarily attempt to emulate the effects of more natural breathing in the patient. Resuscitation involves forcing air or oxygen under appropriate pressure through the patient's natural airway system and into his lungs to inflate the latter at appropriate intervals separated by periods during which such application of air or oxygen under pressure is interrupted (and an external physical pressure may be applied to the patient's chest) to permit the previously applied air to escape from the patient's lungs and the latter to deflate.
The forms of previous resuscitators of greatest interest as background for this invention, commonly called "squeeze bag" or "bag-valve-mask" resuscitators, employ some type of manually compressible and self-restoring bag having the interior thereof in fluid communication with a face mask. In its most primitive conceptual form, such a device could be operated for resuscitation purposes simply by applying the mask to the face of a patient, manually squeezing the bag to force air from the bag through the mask and into the patient's lungs, releasing the squeezing pressure from the bag and removing the mask from the patient's face to permlt escape of air from the patient's lungs. At the same time, the bag would restore itself and thereby self-inflate with fresh atmospheric air through the mask. The bag would then remain in its restored condition until the next bag squeezing operation and such cycle would be repeated as necessary. A squeeze bag resuscitator thus permits a trained person administering treatment to directly control both the quantity of air forced into the patients lungs and the intervals of doing so to best suit the condition of the patient through choice of the extent and timing of squeezing of the bag.
Even relatively early squeeze bag resuscitators soon incorporated various refinements, including employment of resilient squeeze bags adapted to be conveniently held in one hand with the face masks carried more or less directly on the frontal extremities of the bags to increase portability and facilitate use by a single person. A bag fill valve (an inward flow permitting check valve for communicating the interior of the bag with the atmosphere) was introduced to permlt refilling of the bag with fresh air during its restoration phase without removing the mask from the face of the patient, And, in conjunction with the bag fill valve came the evolution of the patient non-rebreathing valve assembly. Such assembly is interposed between the bag and the mask and permits fresh air to move from the bag into the mask during the squeeze phase, but vents to the atmosphere air returned to the mask from the patient's lungs during the bag restoration or restored phases, thereby preventing passage of the expired air into the bag from which it would be forced back into the patients lungs or "rebreathed" during the next squeeze phase.
During the course of development of squeeze bag type resuscitators, it was recognized that it would be desirable to administer oxygen, or at least oxygen enriched air, rather than merely atmospheric air, in treating some resuscitation patients.
Accordingly, the development of practical means for introducing oxygen into the squeeze bag initially entailed providing "oxygen enrichment" for the air drawn into the squeeze bag from the atmosphere during the restoration phase of the bag cycle. A common and still prevalent approach to oxygen enrichment is to provide an elongate tube of relatively large diameter having one end thereof in fluid communication with the fill valve opening of the bag (typically at the extremity of the bag opposite from the non-rebreathing valve and mask) and the other end thereof exposed to the atmosphere, together with a considerably smaller tube extending into the larger tube and coupled with a pressurized oxygen source for continuously releasing oxygen into the air entering and accumulating within the large tube from the atmosphere. Such devices are commonly call "oxygen accumulators" and are effective to introduce a mixture of air reasonably enriched with oxygen into the bag during the restoration phase of its cycle, without significantly increasing the pressure within the bag (since one end of the large tube of the accumulator is in free communication with the atmosphere). Examples of these and other oxygen accumulator resuscitators may be found in U.S. Pat. Nos. 4,501,271, 4,774,941, 4,821,713, 5,067,487, 5,109,840, 5,140,982 and 5,279,289. A notable shortcoming of resuscitators of this sort is that the concentration of the continuously flowing oxygen gas is subject to dilution by the ambient air with which it is mixed.
Further, the advent of the oxygen accumulator squeeze bag resuscitator did not satisfy the need for being able to administer substantially pure oxygen to patients under certain relatively frequently occurring high oxygen demand circumstances, such as resuscitation responsive to cardiac distress or like conditions. The invention disclosed in U.S. Pat. No. 3,796,216, however, represented an early attempt to administer essentially pure oxygen to a subject using a squeeze bag resuscitator. The apparatus disclosed therein included a body member, a squeeze bag, an oxygen inlet, a flapper valve and a face mask. The body member comprises a tubular portion to which the mouth of the squeeze bag is connected. The face mask is joined to the tubular member generally opposite the squeeze bag and an inlet adapted to be connected to a source of breathing gas such as oxygen is provided in the tubular member between the squeeze bag and the face mask. The flapper valve resides in the body member and regulates passage of oxygen from the squeeze bag to the face mask.
Unlike those discussed above, the squeeze bag disclosed in U.S. Pat. No. 3,796,216 is not self-restoring but merely flexible or pliable and is continuously inflated with oxygen via the oxygen inlet. When the bag is sufficiently inflated and it is desired to administer oxygen to the subject, the user squeezes the bag to increase the pressure in the tubular member to a level sufficient to cause the flapper valve to expose a mask inhalation port and cover a mask exhalation port whereby the oxygen is passed into the mask for consumption by the subject. Once the contents of the bag have been depleted via squeezing to an extent that the pressure in the body member is insufficient to overcome the bias of the flapper valve, the valve returns to its normal position covering the inhalation port and exposing the exhalation port. At this time, the subject exhales, his expiratory gases passing through the exhalation port, and the bag reinflates. This process is repeated as necessary to facilitate or restore the patients normal breathing pattern.
A functional weakness of this sort of resuscitator is that it is incapable of dispensing pressurized atmospheric air in the event of failure or exhaustion of the pressurized oxygen supply. Specifically, even if the gas source were disconnected from the gas inlet thereby exposing the inlet to the atmosphere, the squeeze bag is not self-restoring. Hence, it cannot create either the negative pressure required to draw air into the inlet or the positive pressure to expel the air therefrom.
U.S. Pat. Nos. 2,399,643, 2,834,339, 3,196,866, 3,316,903, 3,473,529, 4,037,595, 4,077,404, 4,088,131 and 4,121,580 describe self-distending squeeze bag or similar resuscitators variously capable of administering air, oxygen or a mixtures thereof upon compression of the squeeze bag.
The assignee of the present invention, Respironics, Inc. of Murrysville, Pa., has developed a simplified and compact squeeze bag resuscitator, discussed at greater length hereinafter, which permits the subject to consume essentially pure oxygen. The oxygen is delivered to a first manifold that is in fluid communication with an oxygen reservoir bag, a first flapper valve and a second flapper valve. A length of conduit joins the first manifold with a second manifold and delivers the contents of the squeeze bag from the first to the second manifold. The second manifold carries a third flapper valve for relieving excess pressure in the oxygen reservoir bag, which bag surrounds the conduit and is also sealingly connected at its opposite ends to the first and second manifolds. In addition, a non-rebreathing valve and breathing mask are connected to the second manifold in conventional fashion.
In operation, the first flapper valve regulates gas flow into the squeeze bag and the second flapper valve regulates ambient air flow into the manifold. Under normal conditions, the oxygen initially fills the reservoir bag and, if the squeeze bag is in a restoring phase, oxygen flows past the first flapper valve and into the squeeze bag. Alternatively, if the bag is fully restored and the subject inhales, the oxygen may pass the first flapper valve and flow directly to the subject. If, however, the bag is fully restored and the subject is not inhaling, the third flapper valve operates to vent excess oxygen pressure from the oxygen reservoir bag. The third flapper valve prevents excessively high pressure oxygen from reaching the patient's lungs and causing over-inflation and possible physical damage thereto. This valve additionally serves to limit the effect of incoming oxygen pressure on exhalation resistance commonly known as AutoPEEP (automatic positive end expiratory pressure). When internal resuscitator pressure is increased, AutoPEEP manifests itself in increased pressure on the backside or "patient" side of the non-rebreathing valve which, in turn, correspondingly increases the effort exerted by the patient to exhale.
A disadvantage of providing a third flapper valve in the second manifold, however, is that the inclusion of such an element in the resuscitator apparatus unnecessarily complicates construction and adds to the cost of the apparatus.
It has alternatively been proposed to provide one or more apertures or vents in the oxygen reservoir bag such that the bag itself may vent excess oxygen to the atmosphere. An oxygen reservoir bag is typically formed of flexible plastic material and is generally oblate spheroidal in configuration, the "hemispheres" of which spheroid are joined at an equatorial region by heat sealing or other suitable bonding process. In the past, attempts have been made to form the vents simply by cutting one or more notches from the heat seal band produced at the equatorial region by the bonding process. It has been discovered, however, that to cut notches in the bag compromises the venting performance characteristics of the bag. For instance, at low incoming oxygen flow rates, e.g., when incoming oxygen flow is approximately 5 to 10 liters per minute, depending upon vent geometry, delivered oxygen concentration may be less than desirable under normal resuscitator cycling because atmospheric air may enter the bag with minimal resistance whereupon it becomes mixed with the incoming oxygen. Vent geometry also affects AutoPEEP. Thus, a particular vent geometry may be suitable for delivering satisfactory oxygen concentration at low incoming oxygen flow, yet at elevated incoming flow rates, the user may experience excessive AutoPEEP.
As an alternative to notching the reservoir bag's equatorial heat seal band, Respironics, Inc. has developed a thin reservoir bag whose equatorial region is provided with one or more radially projecting flaplike vents. Nevertheless, that design has been found to engender yet another problem, namely, the limp and protruding flap vents tend to randomly fold over and occlude under working pressure, thereby vitiating the intended effect of continuous and reliable venting of excess oxygen. To overcome this problem, it has been suggested to increase the thickness of the walls of bag including the flap vents themselves. This approach, however, produces undesirable consequences. That is, increasing bag thickness proportionately increases material cost. And, a thicker bag results in a more rigid bag that is less responsive to the pressure fluctuations within the resuscitator apparatus. Thus, a thick oxygen reservoir bag is less able to properly contract and expel its charge of oxygen upon restoration of the squeeze bag from a collapsed to a distended condition.
An advantage exists, therefore, for a squeeze bag type resuscitator including a very thin, highly flexible, yet rugged oxygen reservoir bag capable of readily collapsing and delivering essentially pure oxygen upon demand for oxygen stored in the bag, and of continuously and reliably venting excess oxygen between oxygen demand episodes.
The oxygen reservoir bag of the previously discussed Respironics, Inc. resuscitator is also open at its opposite ends or "poles" whereat it is taped or otherwise adhesively and sealingly secured to the first and second manifolds. So constructed, the oxygen reservoir bag establishes a sealed oxygen chamber about the conduit and between the manifolds. A disadvantage of this arrangement is that the additional materials (e.g., tape or adhesive) and attendant labor required to adhesively secure the opposite ends of the oxygen reservoir bag to the manifolds undesirably contribute to the manufacturing cost of the resuscitator. Moreover, if care is not taken in the attachment of the oxygen reservoir bag to the manifolds, oxygen may unintentionally leak from the system at one or both of the manifolds.
U.S. Pat. Nos. 4,917,081 and 4,919,132 teach pliable breathing gas storage bags connected at their opposite ends to components of respiratory apparatus. The bag in U.S. Pat. No. 4,917,081 requires supplemental attachment means to assure its sealing connection. The bag in U.S. Pat. No. 4,919,132 merely receives smooth tubular inserts having no structure to which the bag may positively and sealingly engage to prevent gas leakage from the bag.
In connection with a resuscitator of the type having an oxygen reservoir bag, an advantage exists, therefore, for an improved system by which the oxygen reservoir bag may be sealingly attached to the resuscitator without resort to adhesive tape or other superfluous fastening means.